Process for bleaching cotton



Patented Mar. 18, 1947 NITED S'E'AES Solvay Process Company, New York, N. Y, a corporation of New York No Drawing. Application September 3, 1943, Serial No. 501,139

2 Claims. 1

This invention relates to improvements in bleaching cellulosic materials, particularly to improvements in the bleaching of cotton.

It is Well known that cellulosic materials such as cotton may be bleached by treatment with aqueous solutions containing alkali metal hypochlorites. While these hypochlorites have been extensively used for bleaching purposes, it is believed they tend to degrade the cellulosic materials, thereby producing inferior Whites and causing yellowing of cotton goods upon aging.

It is an object of this invention to provide a method whereby bleaching of cellulosic materials with alkali metal hypochlorites may be carried out in a more effective manner.

It is a particular object of this invention to provide a method of bleachin cellulosic materials with alkaline hypochlorites wherein the rate of release of the bleaching action is controlled so as to achieve maximum bleaching with minimum degradation of the fiber.

Another object of this invention is to provide improved bleaching compositions.

In accordance with this invention, a cellulosic material is contacted with an aqueous alkaline solution of a hypochlorite containing relatively small amounts of an alkali metal stannate. The presence of the stannate, I have found, controls release of the bleaching action of the hypochlorite so that maximum bleaching effects may be achieved with the employment of a minimum amount of bleaching agent. By operating in accordance with this invention I have found that degradation of cellulosic material normally resulting from subjecting the material to bleaching with hypochlorites is substantially diminished, whereby superior whites are produced and the tendency of the bleached material to yellow minimized.

The hypochlorite bleach employed in accordance with this invention may contain any alkaline hypochlorite, for example alkali metal hypochlorites such as sodium, potassium or lithium hypochlorite; the concentration of the hypochlorites in the alkaline liquor employed may vary widely, for example between about 0.05 and about 2 grams per liter, depending on a variety liquor. Other alkalies, such as tetrasodium pyrophosphate, may also be present in the liquor. Bleaching of the cellulosic material may be carried out by suitably circulating the bleach liquor through the material for an appropriate time, e. g., for 3 to 5 hours, at a temperature between about and about 290 F., temperatures in the neighborhood of F, being particularly suitable. Upon completion of the bleach the liquor may be re-used, provided it contains residual bleaching power, or additional bleaching agent may be added to the liquor, as long as it still contains a portion of the stannate, and the fortifled liquor then employed for further bleaching operations until the effect of the stannate is no longer apparent; I have found the presence of an alkali metal hydroxide in amounts of about 0.25 to 1.0 gram per liter retards decomposition of the stannate, thereby permitting more extended use of the liquor containing this substance.

The results obtained by carrying out the bleaching of cellulosic materials in accordance with my invention establish that the presence of the stannate in the bleach liquors advantageously controls rate of release of the bleaching power, thereby achieving the production of maximum whites with the consumption of a minimum amount of the bleaching agent. Typical results achieved by my invention are set forth hereinbelow.

In the following tables brightness of the cloth was determined by the General Electric reflection meter, which is a photoelectric instrument designed to measure reflectance of samples of the bleached materials to blue light, the results obtained being expressed as percentage reflectance as compared with the reflectance from magnesium carbonate. A brightness of 86 or higher is considered good. The fluidity referred to in the followin tables is a measure of the viscosity of a solution of the bleached cellulosic material in cuprammo-nium solvent and is of importance because of its close correlation with the tensile strength of the solid fiber. The fluidity is expressed in reciprocal poises, so that the lower the fluidity number, the higher the viscosity of the cellulosic fibers and, therefore, the less the degradation of the fibers. The fluidity numbers were determined by testing an 0.5% solution of the material in cuprammonium solvent in standard glass viscosity tubes at 20 C. in the customary manner.

In all the subsequent experiments the bleaching was carried out by heating 10 grams of a kier boiled broadcloth having a thread count of 136 x 60 and a weight of 4 yards to the pound for several hours in 300 cc. of the bleaching liquor at 160 F,

Thefollowing table shows the efiect of sodium stannate in controlling the release of hypochlorite bleaching power:

It will be noted from Table 1 that in the absence of stannate all the available chlorine was consumed at the end of four hours without producing a cloth of satisfactory brightness; liquors containing stannate, however, produced cloth having satisfactory brightness and lower fluidity than those resulting from treatment with the liquors containing no stannate, without consuming the entire amount of available chlorine, so that it is clear the presence of the stannate permitted more advantageous use of the available chlorine.

The following table shows the results of experiments in which dilute sodium hypochlorite was employed as the bleaching agent and bleaching continued until all the available chlorine was consumed. The results, as will be evident, show that by bleaching in the presence of sodium stannate, superior products were produced.

Table 2 that my invention provides a process whereby bleaching of cellulosic materials may be carried out more economically and more advantageously and, hence, my invention will undoubtedly be of interest to those engaged in the bleaching of such products.

Since certain changes may be made in carryin out the above process with-out departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A process for bleaching cotton fabric to a brightness of at least 86, which comprises subjecting the fabric to the action of an aqueous alkaline solution containing an alkali metal hypochlorite and between about 0.10 and about 2 grams per liter of a readily soluble stannate at a temperature between 70 and 200 F.

2. A process for bleaching cotton fabric to a brightness of at least 86, which comprises subjecting the fabric to the action of an aqueous alkaline solution containing sodium hypochlorite, between about 0.10 and about 2 grams per liter of sodium stannate and between about 0.25 and about 1 gram per liter of sodium hydroxide at a temperature between about 70 and about 200 F., withdrawing the solution at the completion of the bleach, adding an additional quantity of an alkali metal hypochlorite to the solution, and employing the fortified solution to bleach further quantities of cotton fabric.

STUART M. ROGERS.

REFERENCES CITED The following references are of record in the file of this patent:

0 UNITED STATES PATENTS Number Name Date N.1N.2 N.3 N.4

1,213,921 Liebknecht et a1 Jan. 30, 1917 1, sno ,00 0,2 0. 0 2,170,103 Barton 8- 1939 9. 1.1. available chlorine at start. .0518 .0518 .0518 .0518 1,765,013 Hershman June 17, 1930 g 3 5551 21333333321??? 3 3 45 2.301137 Kennedy Jan. 5, 1943 Brightness of bleached cloth... 84.8 86.7 87.1 87.6 2,220,682 Kaufimann Nov. 5, 1940 Fluidity of bleached cloth 1.90 1.90 1.61 1.40

FOREIGN PATENTS The following table is illustrative of the ad- 7 Number Country Date vantages in employing sodium stannate, as dis- 228,588 British Feb, 2, 1925 tinguished from other alkalies, in conjunction 113,951 British Oct. 19, 1917 with sodium hypochlorite, the pH of the liquor in 238,305 British Aug. 1'7, 1925 each instance being 10.8. It will be noted that 757,377 French Dec. 26, 1933 the bleach liquor containing sodium stannate pror 565,896 German Dec. 7, 1932 duced the cloth of greatest brightness and low- 330,192 German Dec. 9, 1920 est fluidity. 271,155 German Mar. 5, 1914 Table 3 Alkali None NaaPOa NaOH NazO.2.5Si0; Na SnO;

G. p. 1. available chlorine at start 0.0532 0.0532 0.0532 0.0532 0.0532 G. p. 1. available chlorine after 3 hours 000 000 .000 .000 .000 8.6 10. s 10. s 10. a 10.8 p h 8.5 8.7 9.2 10.7 11.4 Brightness of bleached cloth 84. 8 85. 5 85. 9 86. 5 86. 9 Fluidity of bleached cloth 1.45 2.00 1. 92 2.00 1.41

While the above description has been limited OTHER REFERENCES to employment of alkali metal stannate in accordance with my invention, other readily soluble stannates, i. e., stannates which will form aqueous solutions containing in excess of 25 grams of stannate per liter, may also be used.

. It will be evident from the above description Matthews, Bleaching and Related Processes, Chemical Catalog Co., New York, 1921, pages 341, 342 and 381. (Copy available in Div. 43.)

Certificate of Correction Patent No. 2,417,570. March 18, 1%

STUART M. ROGERS It is hereby certified that error appears in the printed specification of the ab numbered patent requiring correction as follows: Column 3, Table 3, third colu thereof, for the heading reading Na PO read Na PO and that the said Lett Patent should be read with this correction therein that the same may conform to record of the case in the Patent Office.

Signed and sealed this 20th day of May, A. D. 1947.

LESLIE FRAZER,

First Assistant Uommz'ssioner of Patents.

W xmmamaq Certificate of Correction Patent No. 2,417,570. a March 18, 1947.

STUART M. ROGERS It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 3, Table 3, third column thereof, for the heading reading N a PO read Na P0 and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of May, A. D. 1947.

LESLIE FRAZER,

First Assistant Uommz'ssioner of Patents. 

